1. Study and Comparison of MPEG-2 and H
Study and Comparison of MPEG-2 and H.264 main profiles and available transcoding methods
EE 5359
Priyanka Ankolekar

2. Introduction
Development of international video coding standards like MPEG-2 led to a boost in multimedia applications like digital video recording and teleconferencing.
On growing demand for better compression performance led to advanced video coding standards like H.264.
H.264 is superficially similar to MPEG-2
However, there are significant differences in the details.
This project aims to compare the MPEG-2 and H.264 main profiles and to discuss related transcoding methods.

3. MPEG-2
Second of several standards developed by the moving pictures experts group [16].
Used as the format of digital TV signals and direct broadcast satellite TV systems.
MPEG-2 is not optimized for low bit rates like 1Mbps. But it outperforms MPEG-1 at 3Mbps and above.
It is used for higher data rates of 4Mbps (DVD) and 19Mbps (HDTV).
MPEG-2 devices are back compatible with MPEG-1.
MPEG-2/Video is formally known as ISO/IEC and as ITU-T Rec.H.262. [21].

4. MPEG-2 Profiles
A profile is a collection of compression tools that together make up the coding system. A different profile means that a different set of compression tools is available. [22]
There are five profiles in MPEG-2, as summarized below.
MPEG-2 Profiles[16]
Abbr.
Name
Picture Coding
Types
Chroma
Format
Aspect Ratios
Scalable modes SP
Simple
profile
I, P
4:2:0
square pixels, 4:3, or 16:9
none MP
Main profile
I, P, B
SNR
Scalable
SNR (signal-to-noise
ratio) scalable
Spatial
Spatially
SNR- or spatial
scalable HP
High profile
4:2:2 or 4:2:0

5. MPEG-2 Encoder [10]

6. MPEG-2 Encoder (contd.)
DCT: 2 dimensional 8x8 – for intra frames 8x8 pels
– for inter frames 8x8 residual blocks
Quantizer: Quantizes DCT coefficients using a default or modified matrix.
Motion Estimation and Compensation:
In the motion estimation process, motion vectors for predicted and interpolated pictures are coded differentially between macroblocks.
For the motion compensation process integer and half pel resolution motion vectors are used to predict from previously decoded pictures.

7. MPEG-2 Decoder [7]

8. H.264 Developed by the Joint Video Team (JVT).
Achieves MPEG-2 quality compression at almost half the bit rate [7].
Significant coding efficiency, simple syntax specifications, and seamless integration of video coding into all current protocols and multiplex architectures.
Supports various applications such as video broadcasting, video streaming, and video conferencing over fixed and wireless networks and over different transport protocols. [4]

9. H.264 Profiles – Comparison [11]
Each H.264 profile specifies a subset of entire bitstream of syntax and limits that shall be supported by all decoders conforming to that profile.
There are three profiles in the first version: Baseline, Main and Extended. There are four High profiles defined in the fidelity range extensions [19].
Baseline
Extended
Main
High
I and P Slices
Yes
B Slices No
SI and SP Slices
Multiple Reference Frames
In-Loop Deblocking Filter
CAVLC Entropy Coding
CABAC Entropy Coding
Flexible Macroblock Ordering (FMO)
Arbitrary Slice Ordering (ASO)
Redundant Slices (RS)

10. H.264 Profiles – Coding parts [1]

11. H.264 Encoder[9]

12. H.264 Encoder
4x4 integer DCT: Smaller blocksize leads to a significant reduction in ringing artifacts.
Quantization and scan: H.264 standard specifies the math formula for the quantization process.
Deblocking filter: To reduce the blocking artifacts in the block boundaries and to stop the propagation of accumulated coded noise. The filtered image is used in motion compensated prediction of future frames and helps achieve more compression.
Intra prediction: The encoder derives a predicted block based on its prediction with previously decoded samples (for I frames).
Inter prediction:
Performed on the basis of temporal correlation and consists of motion estimation and motion compensation.
Motion vector resolution is ¼ pel
Supports large number of block sizes
Multiple reference pictures (upto 32 previously coded frames).

13. H.264 Decoder [7]

14. Comparison between H.264 and MPEG-2
Algorithm Characteristic
MPEG-2
H.264
General
Motion compensated predictive, residual transformed, entropy coded
Same basic structure as MPEG
Block size
8x8
16x16, 8x16, 16x8, 8x8, 4x8, 8x4, 4x4
Macroblock size
16x16 (frame mode)
16x8 (field mode)
16x16
Intra Prediction
None
Multi-direction, Multi-pattern
Quantization
Scalar quantization with step size of constant increment
Scalar quantization with step size of increase at the rate of 12.5%
Entropy coding
VLC
CAVLC, CABAC
Weighted prediction No
Yes

15. Comparison between H.264 and MPEG-2 (contd.)
Algorithm Characteristic
MPEG-2
H.264
Reference picture
One picture
Multiple pictures
Motion Estimation Blocks
16x16
16x16, 8x8, 8x4, 4x4
Entropy Coding
Multiple VLC Tables
Arithmetic Coding and adaptive VLC Tables
Frame Distance for Prediction
+/- 1
Unlimited forward/backward
Fractional Motion Estimation
1/2 Pixel (MPEG2)
1/4 Pixel
Deblocking Filter
None
Dynamic edge filters
Scalable coding support [2]
Yes, layered picture spatial, SNR, temporal scalability
With some support on temporal and SNR scalability
Bit rates with same quality HD video with resolution (1920 x 1080)
Mbps
7 – 8 Mbps
Transmission rate
2 – 15 Mbps
64 kbps – 150 Mbps

16. Performance comparison between H.264 and MPEG-2 – Simulations
Test streams used: Foreman (CIF), News (CIF), Carphone (QCIF) [26].
Codecs used: MPEG-2 [25] and H.264 [24]
Profiles for which the simulations were run: Main and Simple/Baseline.
Compression ratio = Original file size/Compressed file size
Formula to compute PSNR for MPEG-2 (MAXI = 255)

17. Performance comparison between H.264 and MPEG-2 –Simulation (Foreman)
H.264 Main Profile
H.264 Main Profile
H.264 Main Profile
MPEG-2 Main Profile

18. Performance comparison between H
Performance comparison between H.264 and MPEG-2 –Simulation results (Foreman)
Parameter
MPEG-2
H.264
Input video resolution
352 x 288 (CIF)
fps 30
# frames encoded 90
GOP
I-P-B-B-P-B-B
I-B-B-P-B-B-P
PSNR (Y) (dB)
30.42
37.03
PSNR (U) (dB)
39.1
41.08
PSNR (V) (dB)
39.6
43.81
Bit rate (kbits/second)
481.00
481.06
Original file size (.yuv) (MB)
13.3
Compressed file size (KB)
179
172
Compression ratio
74:1
78:1

19. Performance comparison between H.264 and MPEG-2 –Simulation (News)
MPEG-2 Main Profile
H.264 Main Profile

20. Performance comparison between H
Performance comparison between H.264 and MPEG-2 –Simulation results (News)
Parameter
MPEG-2
H.264
Input video resolution
352 x 288 (CIF)
fps 30
# frames encoded 90
GOP
I-P-B-B-P-B-B
I-B-B-P-B-B-P
PSNR (Y) (dB)
37.02
39.1
PSNR (U) (dB)
41.0
PSNR (V) (dB)
39.02
42.0
Bit rate (kbits/second)
376.00
Original file size (.yuv) (MB)
13.3
Compressed file size (KB)
141
134
Compression ratio
94:1
99.7:1

21. Performance comparison between H.264 and MPEG-2 –Simulation (Carphone)
MPEG-2 Main Profile
H.264 Main Profile

22. Performance comparison between H
Performance comparison between H.264 and MPEG-2 –Simulation results (Carphone)
Parameter
MPEG-2
H.264
Input video resolution
176 x 144 (QCIF)
fps 30
# frames encoded 90
GOP
I-P-B-B-P-B-B
I-B-B-P-B-B-P
PSNR (Y) (dB)
30.46
37.6
PSNR (U) (dB)
36.36
40.9
PSNR (V) (dB)
36.5
41.5
Bit rate (kbits/second)
128
127.6
Original file size (.yuv) (MB)
3.3
Compressed file size (KB)
47.2
45.6
Compression ratio
69.6:1
72.6:1

23. Conclusions from simulations
For the same bit rate and video resolution, the PSNR (dB) values are greater for H.264 encoded videos than for the MPEG-2 encoded videos indicating better video quality. This can be verified from the screen shots.
The compression ratio for H.264 encoded video is also better than that for MPEG-2 encoded video inspite of better quality video in H.264.

24. Transcoding: Introduction
Transcoding is the coding and recoding of digital content from one compressed format to another to enable transmission over different media and playback over various devices [29].
High demand for efficient usage of available bandwidth.
Interoperability between different networks and devices is gaining importance. Transcoding is a step in this direction.
Many legacy systems like digital TVs use MPEG-2. Therefore the need for a transcoding architecture that employs the lower cost of H.264 video and does not require a significant investment in additional video coding architecture.

25. Transcoding: The criteria
To achieve optimum results, the following criteria should be satisfied:
The quality of the transcoded bitstream should be comparable to the one obtained by direct decoding and re-encoding of the output stream.
The information contained in the input stream should be used as much as possible to avoid multigenerational deterioration.
The process should be cost efficient, low in complexity and achieve the highest quality possible.

26. Transcoding: Architectures [7,15] Open Loop Transcoding
Operate in transform domain.
Computationally efficient – since they operate directly on DCT coefficients.
Suffer from drift problem.

27. Transcoding: Architectures [7,15] Cascaded Pixel Domain Transcoding
Drift-free architecture
Concatenation of simple encoder and decoder
Reduced complexity since the encoder reuses the motion vectors along with other information extracted from the input bit stream.

28. Transcoding: Architectures [7,15] Simplified DCT Domain Transcoding
Based on the assumption that DCT, IDCT and motion compensation are all linear operations.
Less memory required as compared to CPDT.
Computationally intensive, since motion compensation is performed in the DCT domain.
Due to linearity assumptions, problem of drift may occur.

29. Transcoding: Architectures [7,15] Cascaded DCT Domain Transcoding
Used for spatial and temporal resolution downscaling.
Greater flexibility as compared to SDDT.
Greater cost and complexity – since additional DCT motion compensation and frame memory is used.
Adopted for downscaling operations where the encoder side DCT-MC and memory will not cost much.

30. References
[1] Soon-kak Kwon, A. Tamhankar and K.R. Rao, “Overview of H.264 / MPEG-4 Part 10 (pp )”, Special issue on “ Emerging H.264/AVC video coding standard”, J. Visual Communication and Image Representation, vol. 17, pp , April 2006.
[2] A. Puri, H. Chen and A. Luthra, “Video Coding using the H.264/MPEG-4 AVC compression standard”, Signal Processing: Image Communication, vol.19, pp , Oct 2004.
[3] Hari Kalva, “Issues in H.264/MPEG-2 Video Transcoding”, Computer Science and Engineering, Florida Atlantic University, Boca Raton, FL.
[4] S. Sharma, “Transcoding of H.264 bitstream to MPEG 2 bitstream”, Master’s Thesis May 2006, EE Department, University of Texas at Arlington.
[5] S. Sharma, K. R. Rao, “Transcoding of H.264 bitstream to MPEG-2 bitstream”, Proceedings of Asia-Pacific Conference on Communications 2007.
[6] “Emerging H.264/AVC Video Coding Standard”, J. Visual Communication and Image Representation, vol.17, pp , April 2006.
[7] P.N.Tudor, “Tutorial on MPEG-2 Video Compression”, IEE J Langham Thomson Prize, Electronics and Communication Engineering Journal, December 1995.
[8] “The MPEG-2 International Standard”, ISO/IEC, Reference number ISO/IEC , 1996.
[9] T. Wiegand et. al., “Overview of the H.264/AVC Video Coding Standard”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 13, Issue 7, pp , July 2003.
[10] J McVeigh et. al., “A software based real time MPEG-2 video encoder”, IEEE Trans. CSVT, Vol 10, pp , Oct.2000.
[11] Morris, O.J., “MPEG-2: Where did it come from and what is it?”, IEE Colloquium, pp. 1/1-1/5, 24 Jan 1995.

31. References (contd.)
[12] Kunzelmann, P.; Kalva, H., “Reduced Complexity H.264 to MPEG-2 Transcoder”, ICCE 2007, pp. 1-2, January 2007.
[13] Kamaci, N., Altunbasak, Y., “Performance Comparison of the Emerging H.264 Video Coding Standard with the existing standards”, ICME, Vol.1, pp , July 2003.
[14] Jun Xin, Chia-Wen Lin, Ming-Ting Sun , “Digital Video Transcoding”,
Proceedings of the IEEE, Vol. 93, Issue 1,pp 84-97, January 2005.
[15] A. Vetros, C. Christopoulos and H. Sun, “Video transcoding architectures and techniques: an overview”, IEEE Signal Processing magazine, Vol. 20, Issue 2, pp 18-29,March 2003.
[16] “MPEG-2”, Wikipedia, 14 February 2008.
Available at <
[17] “Introduction to MPEG 2 Video Compression”
Available at <
[18] “H.264/MPEG-4 AVC”, Wikipedia, 18 February 2008.
Available at <
[19] “H.264 A new Technology for Video Compression” – Available at <
[20] R Periera, “Efficient transcoding of MPEG-2 to H.264”, Master’s thesis Dec 2005, EE Department, University of Texas at Arlington.
[21] “H.262 : Information technology - Generic coding of moving pictures and associated audio
information: Video”, International Telecommunication Union,
Available at <
[22] “MPEG-2 White paper”, Pinnacle Technical Documentation, Version 0.5, Pinnacle Systems, Feb. 29, 2000.

32. References (contd.)
[23] M. Ghanbari, “Standard Codecs : Image Compression to Advanced Video Coding,” Hertz, UK: IEE, 2003.
[24] H.264 software (version 13.2) obtained from:
<
[25] MPEG-2 software (version 12) obtained from:
<
[26] Test streams (Foreman, News, Carphone) obtained from:
<
[27] Implementation Studies Group, “Main Results of the AVC Complexity analysis”, MPEG document N4964, ISO/IEC JTC11/SC29/WG11, July 2002.
[28] A. Joch et al., “Performance comparison of video coding standards using Lagarangian coder control”, Int. Conf. of Image Processing, Vol. 2, pp. II-501 to II-504, Sept
[29] I. Sylvester, “Transcoding: The future of the video market depends on it”, IDC Executive Brief, Nov
Available at <
[30] R. Hoffner, “MPEG-4 Advanced Video Coding emerges”,
Available at <
[31] S. Wagston and A. Susin, “IP core for an H.264 Decoder SoC”, 2007,
Available at<
[32] S. Krishnamachari and K. Yang, “MPEG-2 to H.264 Transcoding: Why and How?”, Dec. 1, 2006,
Available at <